Phone is noticeably warm when it happens, so it's due to something using energy, and the problem appeared suddenly, so it's not due to a failing battery.

Update:

Today it was bad for an hour or two and then became normal (normal is a few percent an hour). You can see the abrupt change in the image below. I don't know why. The battery usage list looks identical to yesterday, so if it's due to an app, it's not a visible app. I realized I could click the graph and see a more detailed one, and it shows "Awake" during the part where the battery is being eaten while the display is off:

Is this a "wakelock"?

I did change the GSM preferences to "Auto mode" instead of "WCDMA preferred", but that was last night and it was still eating the battery quickly this morning for a while.

You may need to wipe and reinstall the ROM. Also, I believe in CM, there is a setting to use 2g when the screen is off. That might help. Also, fyi, CM 10 runs great on the G2. In fact, CM10 runs better on the G2 than on the Sensation, imho.
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rm-vandaJan 24 '13 at 20:18

@rm-vanda: I already have it set to "Use 2G networks" all the time because I don't have a data plan. How do I get CM10 on a G2? I thought it wasn't supported because it would run too slowly.
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endolithJan 25 '13 at 0:07

@Izzy: This is something that's been happening for weeks, despite lots of reboots. Wakelocks look promising, though. I installed BetterBatteryStats so maybe I can find out from that.
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endolithJan 27 '13 at 19:05

1 Answer
1

Batteries degrade over time. My last phone (Samsung Galaxy S Vibrant) would only charge to 93%. It would never charge higher than that. Near the end of my use of the phone the battery would only last about 5 - 7 hours. This is with disabling GPS, WiFi, Bluetooth.

Also, Something has to be the "highest" user of the battery. Since you disabled the stuff that is usually the big users of battery, something else is taking that spot.

Charging forms deposits inside the electrolyte that inhibit ion transport. Over time, the cell's capacity diminishes. The increase in internal resistance reduces the cell's ability to deliver current. This problem is more pronounced in high-current applications. The decrease means that older batteries do not charge as much as new ones (charging time required decreases proportionally).

High charge levels and elevated temperatures (whether from charging or ambient air) hasten capacity loss. Charging heat is caused by the carbon anode (typically replaced with lithium titanate which drastically reduces damage from charging, including expansion and other factors).

A Standard (Cobalt) Li-ion cell that is full most of the time at 25 °C (77 °F) irreversibly loses approximately 20% capacity per year. Poor ventilation may increase temperatures, further shortening battery life. Loss rates vary by temperature: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F). When stored at 40%–60% charge level, the capacity loss is reduced to 2%, 4%, and 15%, respectively.[citation needed] In contrast, the calendar life of LiFePO4 cells is not affected by being kept at a high state of charge

Emphasis mine. But note that it does "not charge as much". Android will still report that the battery is at 100% because it is. It is charged to the full capacity that the battery can handle. This is why it doesn't seem to hold a charge for as long as it used to.

The fact is, your lithium-ion battery starts dying the moment it leaves the factory! Of course, the actual life-span of an unused lithium-ion battery can vary by a fair amount based on its internal charge as well as the external temperature. But suffice to say that you can expect to irreversibly lose 20% of a lithium-ion battery’s charge every year from its original date of manufacture.

Other things can even make these numbers worse. Like frequent discharges, keeping the battery in non-optimal temperatures and leaving the battery "sitting" idle for periods of time.

If you're going to down vote me, how about a reason? My answer is 100% valid. If you look at the percentages of everything that is "using" your battery, they total ~100% (99%, but they don't show partial percentages). The second image totals 102%, again because they round and don't show partials. Something has to use the battery, if you don't want anything to use the battery then you have to turn off the device completely.
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Ryan ConradJan 25 '13 at 20:57

@RyanConrad: The battery usage screen always adds up to 100%. It's telling you the relative proportion of energy used by each app, not the total amount of energy being used.
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endolithJan 27 '13 at 19:00

@RyanConrad: and it's not due to a failing battery, as I said in the question. Some app or background process is using much more energy than it did in the past.
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endolithJan 27 '13 at 19:02

Then that app would show up in the battery usage. The battery is over 2 years old, how do you know the battery isn't degrading. I didn't say failing. All li-ion batteries degrade over time. I had one that would actually discharge faster then it charged (i could only charge it when the device was off)
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Ryan ConradJan 27 '13 at 19:51